1. Field of the Invention
The present invention relates in general to an automatic control of allowing the optimum fine-slow to be performed in a video cassette recorder (VCR), and more particularly to an apparatus and a method for controlling automatically a fine-slow in a VCR wherein a direct current (DC) envelope signal is detected for a slow playback and passed through an analog/digital converter in a microcomputer, thereby allowing the fine-slow to be automatically processed.
2. Description of the Prior Art
In a method of controlling a slow (low speed playback) in a VCR in accordance with the prior art, a control signal is generated from a servo control device in the control of the slow, to allow a video tape to travel in a slow mode. In response to the control signal from the servo control device, a capstan motor allows the video tape to travel at a low speed, thereby causing the VCR to operate in the slow mode. Capstan motor control timing data or tracking data is typically stored as ROM data in the servo control device or generated from a microprocessor in system controller.
In accordance with the control signal for allowing the VCR to operate in the slow mode, a still operation is performed for a predetermined period of time and then a slow playback operation is performed, and these operations are performed repeatedly. In the still interval, a rotation head drum rotates continuously, the video tape not travelling. Namely, in the still interval, the same frame signal is repeatedly played back.
In the slow playback interval, the capstan motor is controlled in three intervals, or GO, NORMAL SPEED and STOP intervals. In the GO interval, the capstan motor is started. In the NORMAL SPEED interval, the capstan motor allows the video tape to travel at a normal speed in the slow mode. In the STOP mode, the capstan motor allows the VCR to stop the fine-slow.
In the GO interval, a relatively high voltage of the control signal is initially generated to make a starting torque of the capstan motor high. After the lapse of a predetermined time period, the capstan motor is driven at the normal speed in the NORMAL SPEED interval. In this NORMAL SPEED interval, a capstan motor control voltage of the control signal is generated such that the video tape travelling speed in the slow mode is 50-70% of that in a normal play mode. In the STOP interval, since the capstan motor may overrun due to an acceleration thereof, a high voltage of the control is generated to drive the capstan motor in reverse to stop it.
However, in the case where the VCR is operated in the slow mode as mentioned above, if the trace of patterns recorded on the video tape is not in accord with that of a video head mounted to a head cylinder due to a tracking swerve, a radio frequency signal on a center track becomes weak, resulting in occurrence of a noise at the lower or upper portion of a screen.
In other words, in the case where the video tape is so positioned that the trace of the patterns (tracks) recorded on the video tape is not in accord with that of the video head, or in the case where the tracking is swerved in a speed change mode because of compatibility relation based on a VHS type or a B type in which the patterns are recorded, the noise may occur at the upper or lower portion of the screen.
For the purpose of removal of the noise on the screen, a tracking up (+)/down (-) key on a remote controller or a switch is utilized to generate a control signal such that the trace of the patterns (tracks) recorded on the video tape is in accord with that of the video head. The use of the tracking up (+)/down (-) key on the remote controller or switch enables the user to watch the optimum video picture on the screen. Nevertheless, it is next to impossible to store slow mode tracking data suitable, respectively, to the video tapes of the various types as ROM data in the servo control device or to program the data in the microprocessor in the system controller. For this reason, in the method of controlling the fine-slow in the VCR in accordance with the prior art, the user must operate the tracking key to set the optimum tracking, so as to watch the optimum video picture on the screen in the slow mode. Moreover, the user may be ignorant of how to use the tracking key in the slow mode. As a result, the user has difficulty in finding the optimum fine-slow.